Genetic identification of monozygotic ("identical") twins: on the brink of possibility

Abstract

The article at an interdisciplinary level deals with the issues of monozygotic twins individualization using forensic DNA identification methods. The problematic area is that STR analysis, which is the basis of expert methods and the creation of genetic databases, produces identical DNA profiles with samples of monozygotic twins. From the perspective of an integrating specialist the legal, statistical and molecular-genetic aspects of the problem are discussed. The consequences of this limitation for the investigation of crimes and legal proceedings in criminal and civil proceedings are demonstrated using examples from practice. It is shown that, given comparable factual circumstances, the court decisions may differ significantly. Data on the frequency of natural birth of monozygotic twins are presented, and a noticeable increase in the frequency of births of monozygotic twins is noted in connection with the use of medical reproductive technologies. It has been substantiated that, despite the initial genetic identity, the accumulation of spontaneous mutations, variability of epigenetic markers, as well as other factors lead to the emergence of differences in monozygotic twins detected by modern technologies. The types of such differences, their molecular mechanisms and prospects for application in criminalistics and forensic medicine for establishing identity and family links are considered. The problems and prospects for further development of identification of monozygotic twins issues are discussed.

References

1. Bochkov, N.P., Zaharov, A.F. and Ivanov, V.I. (1984). Medical genetics (Guidelines for doctors). Moscow (in Russ.).
2. Perepechina, I.O. (2023). Possibilities and problems of monozygothic twins identification by DNA analysis methods in criminalistics and forensic medicine. In: I. Yu. Makarov (Ed.) Forensic medical science and expert practice: tasks, ways of improvement at the present stage. Proceedings of the IX All-Russian Congress of Forensic Scientists with International Participation (November 22–24, 2023, Moscow) (V. 2, pp. 379–386). Moscow (in Russ.).
3. Pritchard, D.D. and Korf, B.P. (2009). Visual medical genetics. Moscow (in Russ.).
4. Abdellaoui, A. et al. (2015). CNV Concordance in 1,097 MZ Twin Pairs. Twin Res Hum. Genet., 18, pp. 1–12.
5. Aston, K.I., Peterson, C.M. and Carrell, D.T. (2008). Monozygotic twinning associated with assisted reproductive technologies: a review. Reproduction, 136(4), pp. 377–386.
6. Bortolus, R. et al. (1999). The epidemiology of multiple births. Hum. Reprod. Update, 5, pp. 179–187.
7. Corner, GW. (1922). The morphological theory of monochorionic twins as illustrated by a series of supposed early twin embryos of the pig. Bull Johns Hopkins Hosp., 22(33), pp. 389–392.
8. Fellman, J. (2013). Statistical analyses of monozygotic and dizygotic twinning rates. Twin Res Hum. Genet., 16(6), pp. 1107–1111.
9. Fu, G. et al. (2023). Feature selection with a genetic algorithm can help improve the distinguishing power of microbiota information in monozygotic twins' identification. Front Microbiol., 14, pp. 1210638.
10. Hur, Y.-M. et al. (2019). Twin family registries worldwide: an important resource for scientific research. Twin Res Hum. Genet., 22(6), pp. 427–437.
11. Hwa, H.L. et al. (2024). DNA identification of monozygotic twins. Forensic Sci. Int. Genet., 69, pp. 102998.
12. Jin, H., Han, Y. and Zenker, J. (2024). Cellular mechanisms of monozygotic twinning: clues from assisted reproduction. Human Reproduction Update, 30(6), pp. 692–705.
13. Jonsson, H. et al. (2021). Differences between germline genomes of monozygotic twins. Nat. Genet., 53(1), pp. 27–34.
14. Galton, F. (1983). Inquiries into Human Faculty and Its Development. London.
15. Krawczak, M. et al. (2012). How to distinguish genetically between an alleged father and his monozygotic twin: a thought experiment. Forensic Sci. Int. Genet., 6, pp. e129-e130.
16. Liu, M. et al. (2025). Current progress and future perspectives in personal identification of monozygotic twins in forensic medicine. Forensic Sci. Int. Genet., 76, pp. 103231.
17. Menga, D. et al. (2023). Distinguishing between monozygotic twins' blood samples through immune repertoire sequencing. Forensic Sci. Int. Genet., 64(3), pp. 102828.
18. Monden, С., Pison, G. and Smits, J. (2021). Twin Peaks: more twinning in humans than ever before. Human Reproduction, 36(6), pp. 1666–1673.
19. Parson, W. et al. (2013). Evaluation of next generation mtGenome sequencing using the ion torrent personal genome machine (PGM). Forensic Sci. Int. Genet., 7(5), pp. 543–549.
20. Pedersen, D.A. et al. (2019). The Danish twin registry: an updated overview. Twin Res Hum. Genet., 22(6), pp. 499–507.
21. Pös, O. et al. (2021). DNA copy number variation: main characteristics, evolutionary significance, and pathological aspects. Biomed. J., 44, pp. 548–559.
22. Rolf, B. and Krawczak, M. (2020). The germlines of male monozygotic (MZ) twins: Very similar, but not identical. Forensic Sci. Int. Genet., 50, pp. 102408.
23. Sun, W. et al. (2024). Technical strategy for monozygotic twin discrimination by single-nucleotide variants. Int J. Leg. Med., 138, pp. 767–779.
24. van der Gaaga, K.J. et al. (2025). Identifying a monozygotic twin brother as a donor of DNA in minimal, mixed forensic stains — A case example. Forensic Sci. Int. Genet., 78, pp. 103292.
25. van Dongen, J., Hubers, N. and Boomsma, G.I. (2024). New insights into the (epi)genetics of twinning. Human Reproduction, 39(1), pp. 35–42.
26. Vidaki A. et al. (2017). Epigenetic discrimination of identical twins from blood under the forensic scenario. Forensic Sci. Int. Genet., 31, pp. 67–80.
27. Wang, L.F. et al. (2015). Tri-allelic pattern of short tandem repeats identifies the murderer among identical twins and suggests an embryonic mutational origin. Forensic Sci. Int. Genet., 16, pp. 239–245.
28. Weber-Lehmann, J. et al. (2014). Finding the needle in the haystack: Differentiating "identical" twins in paternity testing and forensics by ultra-deep next generation sequencing. Forensic Sci. Int. Genet., 9, pp. 42–46.
29. Yuan, L. et al. (2020). Identification of the perpetrator among identical twins using next generation sequencing technology: A case report. Forensic Sci. Int. Genet., 44, pp. 102167.